Topic 6.5 Flashcards
Daily intake of carbohydrates
300g
Main form of intake of carbohydrates
polycarbohydrates
Daily intake of proteins
40-100g
Daily intake of fats
50-100g
Daily intake of dietary fibers
50-100g (not digested)
Daily intake of H20
1.5-2L
Where does digestion mostly take place?
In the small intestine
What are the 3 main mechanisms of digestion?
- Luminal
- Brush border
- Intracellular
What are the 2 mechanisms of absorption?
- Transcellularly
2. Paracellularly
What are the 2 main digestive enzymes in the oral cavity?
amylase and lingual lipase
Difference between lingual lipase and pancreatic lipase?
lingual lipase can chop off al 3 fatty acids from a triglyceric molecule
What can be absorbed in the oral cavity? (4)
- alcohol
- medicines
- nicotine
- dope, narcotics
How much protein digestion happens in stomach
15-20%
What are the 3 digestive enzymes in the stomach?
- pepsinogen (then pepsin)
- gastric lipase
- salivary amilase still working a bit
What are the differences between the salivary and gastric lipases?
they’re the same
Which molecules can be absorbed in the stomach?
lipid soluble molecules like alcohol and medicine
What makes the small intestine so important for digestion and absorption?
its large surface thanks to circular folds, vili, brush border
At what levels does carbohydrate digestion happen in SI?
- Luminal digestion
- Brush border digestion
Examples of plant starch molecules (polycarbohydrates)
- amylopectin
- amylase
Animal starch?
glycogen
What are dietary fibers?
polycarbohydrates that cannot be digested and will be used for the formation of feces
What disaccharides in our diet? (2)
Lactose, sucrose
How are polysaccharides digested?
by being degraded until they are monosaccharides
Which enzyme group digests polysaccharides?
amylase enzymes (mostly pancreatic)
Which bond do amylases cleave?
internal alpha (1-4) bond
What are the 3 products of amylase enzymes?
- maltose
- maltriose
- alpha-limit dextrins
Which enzyme group will further degrade the glucose polymers?
oligosaccharidases in the brush border
4 examples of oligosaccharidases
- maltase
- alpha-dextrinase
- lactase
- sucrase
What does alpha dextrinase form?
glucose
What does maltase form?
glucose
What does lactase form?
galactose + glucose
What does sucrase form?
fructose + glucose
What does SGLT-1 transport?
- Na+
- Galactose or glucose
What type of transport is SGLT-1?
secondary active transport using gradient provided by Na+/K+ pump
What type of transport is GLUT-5?
facilated diffusion
What does GLUT-5 transport?
Mainly fructose, but if needed it can also have glucose and galactose as substrates
What is GLUT-2 transporting?
Glc, Gal, Frct
What type of transport is GLUT-2?
facilated diffusion
How much protein do we have to digest on top of intake?
50g
How much AA is absorbed and how much is left in the feces
97% absorbed and 2% in feces
3 steps of protein digestion in small intestine
- Luminal phase : pepsin or pancreatic proteases
- Brush border : proteases
- Peptidases (inside cell)
What are trypsin inhibitors useful for?
They inhibit the autocatalytic activity of trypsinogen so it can’t activate itself
Which enzyme converts trypsinogen to trypsin?
enterokinase, aka enteropeptidase
How much protein is absorbed in the form of AA and in the form of di/tripeptides?
AA : 70-75%
Di/tripeptide : 25-30%
How are single AA taken up by enterocytes?
coupled with Na+
How are di/tripeptides taken up by enterocytes?
coupled with H+ with PepT1 co transporter
How much protein can be taken up intactly by the enterocytes?
Around 1milllionth (200g / n.cm²)
How many lipids are added on for digestion due to desquamation?
10-12g
How are lipids digested?
1 step : luminal, using gastric, lingual and pancreatic lipases
3 isoforms of lipases?
- Lipase
- Esterase
- Phospholipase A2
What does lipase convert
triglyceride to 2 monoglyceride and FA
What does PLA2 convert
lecithin to FA + lysolecithin
What does esterase convert
Cholesterol ester to FA + cholesterol
How are bile acids absorbed? (2)
- If conjugated : Na+/bile salt symporter
2. Not conjugated : diffusion
What are the 4 ways of absorbing Na?
- nutrient coupled absorption (glucose, AA)
- Electroneutral Na/H exchange
- Parallel Na/H and Cl/HCO3- echangers
- Epithelial Na channel
Average daily intake and absorption of Ca
1g and 0.4g
Entire iron pool of the body
4g
Iron loss / day
0.1g/day
2 ways or iron absorption
- organically : in the form of heme then Fe
- inorganically : Fe2+ form by a metal transporter
2 vitamin groups
- fat soluble : A, D; E and K
2. Water soluble : C, B1, B6, B13
How are fat soluble vitamins absorbed?
Passive absorption
How are water soluble vitamins absorbed?
Na+ dependant transport
Which cells release the intrinsic factor?
Parietal cells
